1. Field of the Invention
The present invention relates to rocket deceleration systems and more particularly to the utilization of canted rockets for the attenuation of spacecraft velocity.
2. Description of the Related Art
Recovery of entry spacecraft from earth orbit has, for the United States, been accomplished by landing at sea, after deploying parachutes to reduce the vertical velocity to approximately 30 feet/second. Activities involved with the Assured Crew Return Vehicle (ACRV) Program involved the evaluation of land landing concepts. As will be described in details below, the present invention involves the use of retrorockets as the most promising approach to recovery of capsule-type vehicles, with the Apollo Spacecraft being an example. The key problem in such a re-entry technique was to fully attenuate both the vertical velocity, which is relatively constant at 30 fps, using three (Apollo) parachutes, and the horizontal velocity which was deemed to vary from zero to 53 fps (36 mph), depending on wind conditions. Other design criteria included the possibility that the vertical velocity could rise to 35 fps in the event of chute failure and 50 fps with two chutes out. Finally, an unlikely failure of one or two retrorockets could occur. It was decided that rotation of the capsule about its vertical (roll) axis would not be controlled. The goal, then, was to devise a retrorocket system that would respond to all of the variables: wind velocity, chute failures, and rocket failures, yet touch down at substantially zero vertical and horizontal velocities.
Prior art attempts to accomplish these goals were unsuccessful. For example, attempts have been made to slide on inflated bags across the landing site. But this would have required a prepared site, a constraint to be avoided, if possible. Also, the bags required tended to position the spacecraft so high above the ground that tipover of the entire assembly was considered a significant risk. Russia has successfully demonstrated ground landings for several years, using six rockets, but they can neither compensate for winds, nor can they land gently in order to accommodate a seriously ill crewman, or in spite of a failed chute. And last, crushable structures, such as honeycomb or foam were evealuated. Obviously, these would work only on a virtually windless day, with all chutes and rockets operating properly.